Aggregate travel vs. single trip assessment: arguments for cumulative risk analysis.

Vaccine recommendations for travellers are based on individual risk assessments of multiple factors, most importantly the destination and duration of the impending trip. Many people undertake frequent trips, but existing WHO, CDC and national advisory board recommendations do not explicitly consider cumulative travel-associated risks. Given the period of protection provided by many vaccines, in particular rabies, hepatitis A, hepatitis B and yellow fever vaccines, an aggregate multi-trip risk assessment which views vaccines as an investment for future travel health may be more appropriate than separately evaluating the risks for each trip.